The present invention relates to thermoplastic compositions of fluoropolymers having a reduced smoke release when subjected to a heat source. Said thermoplastic compositions are used in the xe2x80x9cplenum wire insulationxe2x80x9d and xe2x80x9ccable jacketingxe2x80x9d field, where lower and lower values of xe2x80x9caverage smokexe2x80x9d and xe2x80x9cpeak smokexe2x80x9d according to the UL910 Steiner Tunnel test are required.
More specifically the present invention relates to thermoplastic compositions of fluoropolymers of ethylene (E) with tetrafluoroethylene (TFE), and/or chlorotrifluoroethylene (CTFE), modified with one or more hydrogenated monomers.
Said fluoropolymers are used in the manufacture of flexible cables. An essential feature of these fluoropolymers consists in that they do not show a xe2x80x9cnecking at yieldxe2x80x9d on the stress-strain curve, thus avoiding the xe2x80x9cwhiteningxe2x80x9d effect on the bent cable, which visually represents the permanent plastic deformation suffered by the material.
From EP 866, 079 in the name of the Applicant, copolymers of ethylene with tetrafluroethylene and/or chlorotrifluoroethylene, modified with hydrogenated monomers, are known, the flexibility (low elastic modulus) is conferred by formulating them in compositions comprising hydrogenated plasticizers. These compositions when subjected to a heat source show a substantial decrease of smoke when the inorganic fire-retardants described in EP 906,934 in the name of the Applicant.
However in the various industrial applications, for example cable jacketing, compositions with lower and lower smoke emissions are required for clear safety reasons. Furthermore the rules regulating smoke emission become more and more restrictive in various Countries.
Therefore a further lowering of the xe2x80x9caverage smokexe2x80x9d and xe2x80x9cpeak smokexe2x80x9d values with respect to the materials of the prior art is desired and required by the cable industry.
The need was felt to have available fluorinated polymer compositions based on ECTFE or ETFE, showing a reduced smoke release, determined as xe2x80x9caverage smokexe2x80x9d and as xe2x80x9cpeak smokexe2x80x9d according to UL910 Steiner Tunnel, with respect to those of the prior art, so that it were possible to use said compositions as jacketing in cables containing primary cables formed of various materials (hydrogenated polymers, for example polyethylene, and/or fluorinated polymers, for example TFE-hexa-fluoropropene copolymers (FEP)) which were more reliable in case of fire.
The Applicant has surprisingly and unexpectedly found that by using in polymer compositions comprising ECTFE or ETFE polymers modified with hydrogenated monomers, fire-retardants agents together with crosslinking agents, it is possible to obtain compositions having a lower smoke release, determined both as xe2x80x9caverage smokexe2x80x9d and as xe2x80x9cpeak smokexe2x80x9d (UL910 Steiner Tunnel), with respect to those of the compositions of the prior art.
An object of the present invention is a polymer composition formed by:
I) fluoropolymers selected from one or more of the following: copolymers based on ethylene, TFE and/or CTFE, modified with hydrogenated monomers, or blends of these fluoropolymers with homopolymers of CTFE or (co)polymers based on CTFE (PCTFE) containing at least 99% by moles of CTFE, the complement to 100 being one or more fluorinated monomers or hydrogenated monomers; said fluoropolymers and/or the corresponding blends optionally mixed with hydrogenated plasticizers;
II) one or more inorganic fire-retardants, optionally treated with dispersing agents;
III) one or more crosslinking agents;
IV) optional additives such as fillers, xe2x80x9cintumescent agentsxe2x80x9d, pigments, lubricants, organic xe2x80x9cfire-retardantsxe2x80x9d and thermal stabilizers.
More specifically the fluoropolymers component I) of the composition object of the invention are formed by the following monomers:
(a) ethylene from 10 to 70%, preferably from 35 to 55% by moles;
(b) a fluorinated monomer selected from tetrafluoroethylene, chlorotrifluoroethylene, or mixtures thereof, in a percentage by moles in the range 30-90%, preferably 45-65%;
(c) from 0.1 to 30%, preferably from 1 to 15%, by moles with respect to the total amount of (a)+(b), of a hydrogenated monomer of formula:
CH2xe2x95x90CHxe2x80x94(CH2)nxe2x80x94R1 xe2x80x83xe2x80x83(I) 
wherein R1=xe2x80x94OR2, xe2x80x94(O)tCO(O)pR2 wherein t and p are integers equal to 0 or 1, and R2 is a hydrogenated radical from 1 to 20 carbon atoms, linear and/or branched, or cycloalkyl, C1-C20 alkyl radical, or R2 is H. The R2 radical can optionally contain: heteroatoms preferably Cl, O, N; one or more functional groups preferably selected from OH, COOH, epoxide, ester and ether; and double bonds; n is an integer in the range 0-10. Preferably R2 is an alkyl radical from 1 to 10 carbon atoms containing one or more hydroxide functional groups and n is an integer in the range 0-5.
The comonomers (c) are for example selected from the following classes:
1) Acrylic monomers of formula:
CH2xe2x95x90CHxe2x80x94COxe2x80x94Oxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Among the monomers which have the formula reported in 1) can be mentioned for example: ethylacrylate, n-butylacrylate, acrylic acid, hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy) ethylhexylacrylate, acryl (N-alkyl) amide wherein alkyl is C1-C5, etc.
2) Vinylether monomers of formula:
CH2xe2x95x90CHxe2x80x94Oxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Among the monomers which have the formula reported in 2) can be mentioned for example: propylvinylether, cyclohexylvinylether, vinyl-4-hydroxybutylether, etc.
3) Vinyl monomers of the carboxylic acid of formula:
CH2xe2x95x90CHxe2x80x94Oxe2x80x94COxe2x80x94R2 
wherein R2 has the above mentioned meaning.
Among the monomers which have the formula reported in 3) can be mentioned for example: vinyl-acetate, vinylpropionate, vinyl-2-ethylhexanoate, etc.
4) Unsaturated carboxylic acids of formula:
CH2xe2x95x90CHxe2x80x94(CH2)nxe2x80x94COOH 
wherein n has the above mentioned meaning. Vinylacetic acid, etc. can for example be mentioned.
The preferred class of monomers (c) are acrylic monomers 1), the most preferred is n-butyl acrylate.
The preferred fluorinated monomer (b) is chlorotrifluoroethylene.
The PCTFE percentage in the blends is in the range 1-75% by weight, preferably 5-30% by weight.
The PCTFE is a semicrystalline (co)polymer of chlorotrifluoroethylene (CTFE) containing at least 99% by moles of chlorotrifluoroethylene where the complement to 100% is formed by one or more hydrogenated monomers, preferably acrylic, or fluorinated monomers, preferably selected from (per)fluoroalkylvinylethers, (per)fluorodioxoles. Preferably the PCTFE is the CTFE homopolymer.
PCTFE and PCTFE blends with the copolymers based on ethylene, TFE and/or CTFE modified with hydrogenated monomers, are obtained according to European patent applications No. 01101784.5 and No. 01101785.2 in the name of the Applicant, herein incorporated by reference.
As component I) fluoropolymers in blend with PCTFE are preferred.
The hydrogenated plasticizers used in mixture with the fluoropolymers component I) of the present invention are those of the prior art, which are used in mixture with hydrogenated (co)polymers; their percentage by weight, based on the total weight of the composition of the present invention, is in the range 0.1-10%, preferably 0.5-5%.
Non limitative examples of said plasticizers are the following: 2-ethylhexyldiphenylphosphate, neopentyl glycoldibenzoate, tricresylphosphate, acetyl-tri-n-butyl citrate (Citroflex(copyright) A4), tributyl trimellitate, tetrabromophthalic ester, tri-n-hexyl-trimellitate (Morflex(copyright)560), ethylene glycol monostearate, acetyl-tri-n-hexyl citrate, di-butoxyethyl adipate (Plasthall(copyright)203); the following are preferred: acetyl-tri-n-butyl citrate, tributyl trimellitate, tri-n-hexyl-trimellitate, di-butoxyethyl adipate.
The xe2x80x9cfire retardantsxe2x80x9d component II) of the composition of the invention are inorganic compounds and their percentage by weight is in the range 0.1-35%, preferably 0.5-15% based on the total weight of the composition.
Examples of these components are inorganic phosphates (for example ammonium phosphate), metal oxides (for example aluminum oxide, trihydrate aluminum oxide, antimony oxides, molybdenum oxide, zinc oxide), tin oxalates, boron compounds (for example borax, zinc borate, Firebrake(copyright)ZB), metal hydroxides, for example magnesium hydroxide, ZnSn(OH)6, etc.
Preferably component II) is treated with dispersing agents.
The preferred dispersing agents according to the present invention are those having the general formula 
wherein A is an atom selected from Si, Ti or Zr, X is a hydrolyzable group, the two free valences being saturated with R or X, R is an oligomer of hydrogenated monomers, or R is equal to R3, R3 being an alkyl C1-C15 and/or aryl radical C6-C15. The R3 radical can optionally contain: unsaturations; one or more heteroatoms selected from O, N, S, Cl; functional groups such as for example amines, epoxide, xe2x80x94SH, xe2x80x94OH, xe2x80x94CONH2, carboxyl or salified carboxyl.
The preferred dispersing agents, in monomeric or oligomeric form, have the following structure:
(R3)4-mA(X)m 
wherein m=1-3, preferably m=2 or 3; X is an hydrolyzable group, preferably X is an alkoxy group OR4 wherein R4 is a linear or branched alkyl radical C1-C5; R3 and A are as above defined. Preferably A is an atom selected from Si or Ti. When A is Si preferably m=3 and R3 is methyl or ethyl.
The preferred dispersing agents are selected from one or more of the following: vinyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-chloroisobutyltriethoxysilane, 3-mercaptopropyltriethoxysilane, octyltriethoxysilane, diisopropoxytitanium bis-acetylacetonate.
The addition of the dispersing agents to the inorganic xe2x80x9cfire retardantsxe2x80x9d is carried out at room temperature. Subsequently the mixture is heated at about 100xc2x0 C. for one or more hours. The water necessary to hydrolyze the X groups in the above reported formula of the dispersing agents is supplied by the reaction medium or by the residual humidity of the organic solutions that contain the dispersing agents. The amount of the crosslinking agent component III) in the composition according to the present invention, as percentage by weight, is in the range 0.05-10.0%, preferably 0.1-5.0%, still more preferably 0.5-2.0%.
The crosslinking agents component III) of the composition object of the present invention are compounds containing at least two double bonds. For example they can be selected from the following: triallylisocyanurate (TAIC), triallylcyanurate (TAC), diallyl-isophthalate (U.S. Pat. No. 4,039,631), diallylterephthalate (U.S. Pat. No. 4,039,631), phenylindene esters (esters of phenyl indan) (U.S. Pat. No. 3,763,222), triallylester of the aryl-polycarboxylic acid (U.S. Pat. No. 3,840,619), bis-olefins such as for example 1,6 divinylperfluorohexane (U.S. Pat. No. 5,612,419) and others (U.S. Pat. No. 4,121,001), diacrylates and triacrylates.
The preferred crosslinking agent is triallylisocyanurate.
The optional ingredients component IV) of the composition according to the present invention are for example fillers (for example polytetrafluoroethylene (PTFE), silicates), lubricants, pigments, organic xe2x80x9cfire retardantsxe2x80x9d compounds (for example halogenated compounds such as chloroparaffins, brominated polyesters, brominated epoxy oligomers), xe2x80x9cintumescent agentsxe2x80x9d, thermal stabilizers such as for example Irganox(copyright) 1010, Mark-260(copyright) (hindered phenols), Aclyn-316(copyright) (acid scavenger).
The amount of the optional component IV) is in the range 0-30% by weight based on the total weight of the composition.
The total sum of the percentages of components I), II), III) and IV) optional being the 100% by weight.
The preferred polymer compositions of the invention comprise the preferred components of I), II) and III).
Preferably the polymer composition has an elastic modulus lower than 1,000 MPa determined according to ASTM D1708 at 23xc2x0 C. and therefore is a flexible polymer composition.
The following Examples illustrate the invention with non limitative purposes.